JPS638937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method of cyanoethylation.
The related method is continuous. What is cyanoethylation?
This is a reaction between acrylonitrile and various compounds to produce β-substituted propionitrile derivatives. These compounds are characterized by having unstable hydrogen atoms. A postplasm is a hydrogen atom bonded to an electronegative atom or to an atom activated by a strongly electronegative substituent. The class of compounds containing labile hydrogen includes those with hydroxyl groups, such as water, alcohols and glycols. Cyanoethylation can be generalized by the following reaction formula.

_{CH2 =} CHCN+RH= _RCH2CH2CN Cyanoethylation products are useful intermediates in the production of plastics and fibers.

Cyanoethylation is used to produce a wide variety of mono- and polyfunctional nitriles. For example, Encyclopedia of Chemical Technology, Kirk-Othmer, 2nd edition, Volume 6, and "Organic Reactions" by Earl Adams et al.
Volume 5, John Willey & Sons, Inc.
See NY 1949.

For large-scale production of β-substituted propionitrile derivatives, it is advantageous to operate the cyanoethylation reaction in a continuous manner. However, it is difficult to do this economically while still obtaining high yields. The reason is (1)
that the cyanoethylation reaction is highly exothermic;
This is because (2) acrylonitrile tends to polymerize when present in high concentrations, and (3) the cyanoethylation reaction is easily reversible under certain conditions. In order to solve the above problem, it is possible to gradually add acrylonitrile to the excess amount of the compound containing unstable hydrogen atoms. However, the latter is relatively inefficient due to the long residence times required to achieve a high degree of conversion.

Overcoming the above problems is the present invention as an improvement to continuous cyanoethylation processes. This improved method provides high yields of β-substituted propionitrile derivatives that can be continuously cyanoethylated in a controlled manner. This high yield is surprising since it is known that under typical operating conditions cyanoethylation reactions can easily become reversible. The improved method also eases the heat removal problem. Additionally, the improved process reduces, if not eliminates, the need for inert solvents.

The improvements in this continuous cyanoethylation method are:
A relatively large portion of the reaction effluent is recycled to the reaction zone. The amount of recirculated effluent is in the range of about 50 to about 90% by weight. The recycle stream is mixed with the fresh charge to the reaction zone prior to its introduction into the reaction zone. The components of the new charge are acrylonitrile, a compound containing labile hydrogen atoms, and a catalyst, if used. Generally, the effluent contains less than about 3% by weight unreacted acrylonitrile and more than about 90% by weight β-substituted propionitrile derivative. The temperature of the reaction zone is within the cyanoethylation reaction temperature range. Commercially, the temperature range is between about 0°C and about 100°C. The catalyst, if used with the system, ie, the reactants, is of homogeneous nature.

The accompanying figure schematically depicts one embodiment of an improved continuous cyanoethylation process.

In the figure, acrylonitrile preparation 1 is the reaction means 10.
will be introduced to Accompanying the acrylonitrile charge 1 is stream 6 whose components are labile hydrogen-containing compound 4, catalyst 5 (if used), and recycle stream 2 which is part of the reaction effluent 8. The remainder of the reactor effluent 3 contains unreacted acrylonitrile,
Processing is performed to separate the desired β-substituted propionitrile derivative from by-products, reaction intermediates, and catalyst (if used).

Reaction means 10 is designed to provide a residence time for the reactants, catalyst (if used), and products to produce the desired conversion. Means 10 may also include means (not shown) for mixing the materials in contact. Also, means 10
may also include an optional means 7 for cooling the cyanoethylation reaction. Residence times generally range from about 15 minutes to about 5-7 hours. Another way to indicate residence time is the composition of the effluent. The effluent leaving the cyanoethylation reaction zone is generally 3
Contains less than % by weight and preferably less than 1% by weight of unreacted acrylonitrile. Another measure of residence time is the amount of desired product in the effluent. The effluent generally contains at least 90% and preferably at least 95% by weight of the desired product.

The amount of recirculation flow 2 lies between two limits. The upper limit is that selectivity decreases as the amount of recycle stream 2 is increased. The lower limit is that when the amount of recycle stream 2 is reduced, the temperature at the inlet of the reaction zone increases, which often results in an increase in the amount of unwanted by-products. The temperature of recirculating stream 2 can be determined by any means (not shown)
Can be changed by Small changes in selectivity and/or temperature can occur for a variety of reasons, so the increase or decrease can be substantial. Commercial ranges for the amount of recycle stream 2 range between about 50% and about 90% by weight of the effluent leaving means 10, with a preferred range between about 60% and about 80%. be.

The cyanoethylation method can also be described as follows. Acrylonitrile 1 at a rate of 613 pounds per hour
is injected into the means 10. Immediately prior to injection into means 10, ethylene glycol 4 at a rate of 358 pounds per hour.
is injected into one part of acrylonitrile, and the ethylene glycol is injected with five parts of sodium hydroxide at a rate of 29 pounds per hour. For the mixture of ethylene glycol and sodium hydroxide, reactor effluent 22000
A pound is also contacted and the resulting three component mixture is contacted with one part of acrylonitrile. Product mixture 3 is removed from the system at a rate of 1000 pounds per hour. The product mixture 3 is sent to purification means, where the catalyst is neutralized and the desired product is separated, for example by distillation. The neutralized product consists essentially of 3,3'-ethylenedioxybis(propionitrile) in excess of 95% by weight. The product yield is greater than 95% by weight based on the ethylene glycol 4 and acrylonitrile charged to the reaction means 10.

Thus, an improvement to the continuous, homogeneous cyanoethylation process when the temperature of the reaction zone equivalent to means 10 above is maintained within the cyanoethylation reaction temperature range is to recycle the reaction effluent to the cyanoethylation reaction zone. Selectivity decreases when the recirculation rate increases above about 90% by weight, and when the effluent recirculation rate increases to about 50% by weight.
This consists in having a recycle amount in the range between when the temperature at the inlet of the reaction zone decreases below the weight percent and when the temperature at the inlet of the reaction zone increases.

Generally, the cyanoethylation reaction temperature ranges between about 0°C and about 100°C. At lower temperatures, the reaction rate is probably too low, while higher temperatures promote undesirable side reactions. The preferred temperature range for the reaction is from about 20°C to about 50°C.

The improved process further provides that a portion of the reaction effluent, which is the effluent from the reaction zone that is not treated to separate the desired β-substituted propionitrile derivatives, contains labile hydrogen atoms. and the resulting mixture of both is contacted with acrylonitrile. The latter is fresh acrylonitrile charged to the reaction zone. The improved process further comprises contacting the resulting mixture of recycled reaction effluent and compounds containing labile hydrogen atoms with a basic catalyst before contacting the acrylonitrile entering the reaction zone.

As is well known, very strong basic catalysts are often used in cyanoethylation reactions. However, it depends on which particular compound containing labile hydrogen atoms is used. Thus, for example, in the case of aliphatic monohydric or polyhydric alcohols a strong base catalyst is used, but if the compound is a primary or secondary aliphatic amine no catalyst is used. Furthermore, as is well known, under certain circumstances acids act as catalysts. The amount of catalyst required is small. Generally, 1 to 5% by weight catalyst based on the weight of acrylonitrile is sufficient. Useful catalysts include alkali metals, alkali metal oxides and alkali metal hydroxides. With alkali metal hydroxides, e.g. KOH
NaOH is often a concentrated aqueous solution.

As already mentioned, one of the reactants in the cyanoethylation reaction is a compound containing labile hydrogen atoms. Thus, reactions can be carried out with hydroxyl compounds such as water, alcohols, polyhydric alcohols, and phenols, thiols such as aliphatic mercaptans, nitrogen compounds such as amines, amides, and many other materials. Polyhydric alcohols include ethylene glycol and the like.

The following examples, along with comparative experiments, illustrate the improved method.

EXAMPLE This example is a batch experiment with simulated recycle flow that demonstrates that the cyanoethylation reaction can be controlled and that high yields of the desired product can be achieved.

248 g of ethylene glycol and 20 g of 40% aqueous NaOH were added to a 2000 ml flask equipped with a stirrer, reflux condenser, and addition funnel and placed in an ice water bath. Start the stirrer and add the acrylonitrile
424 g was added to the funnel over approximately 15 minutes.
The temperature remained in the range 25-35°C during the addition of acrylonitrile. Stirring was continued for another hour, after which 170 g of the reaction mixture was removed from the flask and
Neutralization was achieved by contacting with 70 g of sulfonic acid resin. The mixture removed contained more than 95% by weight of 3,3'-ethylenedioxy-bis(propionitrile) and was almost completely free of acrylonitrile.

The following were quickly added to the flask containing the remaining reaction mixture in the following order. 62 g of ethylene glycol, 5 g of 40% NaOH aqueous solution, and 106 g of acrylonitrile. During the addition the temperature is approximately 30
It stayed at ℃. Then, stirring was continued for 90 minutes. The flask contents were then neutralized with sulfonic acid resin as described above. This second batch of composition was virtually the same as the initially drawn mixture in that it contained more than 95% by weight of propionitrile derivative and almost no acrylonitrile.

In contrast, the following illustrates a particularly rapid exotherm problem encountered during cyanoethylation. To a 500 ml Morton flask equipped with a stirrer, reflux condenser, and addition funnel and placed in an ice water bath, 62 g of ethylene glycol and 5 g of 40% aqueous NaOH were added. 106 g of acrylonitrile was added to the resulting mixture through the funnel and the stirrer was then started.
Within 5 minutes the temperature rose rapidly to 60°C and then to 120°C, at which temperature the contents erupted from the flask.

In a separate experiment, the cyanoethylation reaction was carried out continuously in a 1/4 x 84 inch stainless steel tube reactor immersed in a circulating bath controlled at 30°C. The simulated product ethylene-dioxybis(propionitrile), recycled from the reactor outlet, was pumped into the mixing tee at 0.247 ml per minute.
It was then combined with ethylene glycol containing 7% by weight of a 40% aqueous sodium hydroxide solution pumped at a rate of 0.0285 ml per minute. Mixed flow 1/4
x 20 inch tubing to the second tee and acrylonitrile was pumped at 0.0741 ml per minute or 1.09 moles per mole of glycol. This mixed stream entered the reactor directly and was collected after discharge in a graduated receiver, from which sample cuts were periodically removed. The samples were neutralized by shaking with sulfonic acid ion exchange resin and then analyzed by gas chromatography.

A sample taken after 3 hours contained 93% by weight dinitrile, 1% by weight mononitrile and 1% by weight. The remainder was water from the catalyst and excess acetonitrile. This analysis corresponds to a selectivity of 97% by weight to useful products. Another sample removed after 4 hours was virtually identical, indicating that steady state operation had been reached.

Another series of reactions was carried out in the same manner as above, except that acrylonitrile was injected at 0.0667 ml per minute. Samples taken at 3 and 4 hours of operation were analyzed as before. These contained 95-96% by weight dinitrile, 0.5% mononitrile, 0.5-1.0% other by-products, and 3-4% water, with residual acrylonitrile. The selectivity for the reaction was 97-98% by weight.

Use of other compounds containing labile hydrogen, such as ammonia, amines, water, ethanol, propanol, 2-ethyl-1-hexanol, etc., would have produced similar results.

[Brief explanation of the drawing]

The drawing is a schematic diagram of one embodiment of an improvement in a continuous cyanoethylation process. 1... Acrylonitrile charge, 2... Recycle stream, 3... Reactor effluent, 4... Compound containing unstable hydrogen, 5... Catalyst, 6... Stream, 7...
Optional means for cooling, 8...reaction effluent,
10...Reaction means.

Claims (1)

Claims: 1. A dihydric alcohol is reacted with acrylonitrile and a cyanoalkylation catalyst in a reaction zone at a cyanoalkylation temperature to form a cyanoalkylated dinitrile product, and at least 90% by weight of said dinitrile product is A process for the cyanoalkylation of dihydric alcohols, which involves withdrawing the containing effluent from the reaction zone, tends to involve undesired reactions and thus result in a decrease in selectivity towards the desired dinitrile product. 50-90% of the effluent is recycled to the reaction zone,
This allows the reaction to be carried out in the presence of additional dinitrile product than that produced in situ by the reaction of alcohol and acrylonitrile, thereby reducing the formation of undesired reaction products. A method characterized by: 2 The reactor effluent contains approximately 90% of the cyanoethylated product.
% by weight. 3. The process of claim 2, wherein the reactor effluent contains less than about 3% by weight unreacted acrylonitrile. 4. The method according to claim 1, wherein the reaction temperature is in the range of 0 to 100°C. 5. Process according to claim 4, comprising contacting the recycled reaction effluent with a dihydric alcohol containing labile hydrogen atoms and contacting the resulting mixture with acrylonitrile entering the reaction zone. 6. A process according to claim 5, comprising contacting the mixture of circulating reactor effluent and dihydric alcohol with a basic catalyst before contacting with acrylonitrile. 7. The method according to claim 6, wherein the basic catalyst is selected from the group consisting of alkali metals, oxides of alkali metals, and hydroxides of alkali metals. 8. The method of claim 7, wherein the alkali metal hydroxide is in an aqueous solution. 9. The method according to claim 8, wherein the dihydric alcohol is ethylene glycol. 10. Claim 9 wherein the reactor effluent contains less than about 3% by weight of unreacted acrylonitrile and more than about 90% by weight of 3,3'-ethylenedioxybis(propionitrile). the method of. 11. The method of claim 9, wherein the amount of reactor effluent that is recycled is within the range of about 60% to about 80% by weight of the total amount of reactor effluent. 12 In a continuous, homogeneous cyanoethylation process in which the reaction zone temperature is maintained within the range of about 0°C to about 100°C, the reactants are acrylonitrile and ethylene glycol, and the catalyst is an aqueous alkali metal hydroxide solution. and the amount of reaction effluent recycled to the cyanoethylation reaction zone is within the range of about 60% to about 80% by weight of the total reactor effluent, and the effluent contains less than about 3% by weight of unreacted acrylonitrile. and greater than about 90% by weight of 3,3'-ethylenedioxybis(propionitrile).